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Download Experiment to estimate the value of Planck's Constant 2AN
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2AN Experiment to estimate the value of Planck's Constant using the Photo-Electric Effect 1. Preparation: a) Revise the basic ideas of quantum theory, especially Einstein's photo-electric equation. b) See below. 2. In this method, light is allowed to reach a photo-emissive surface (inside a “photo-cell”). This causes electrons to be emitted with a range of kinetic energies. A “stopping voltage” is then used to stop even the most energetic of the emitted electrons before they reach the cathode of the photo-cell. A simplified diagram of the apparatus is shown below. filter photo-electric cell white light G very sensitive “light beam” galvanometer variable voltage source (voltage = Vs ) Find the voltage, V s , needed to reduce the reading of the galvanometer to zero with a range of different frequencies of light, f, reaching the photo-cell (different coloured filters). Einstein’s photo-electric equation can be stated as eVs = hf – W Use this to find a value of Planck’s constant, h. © David Hoult 2001
